At present, the digital radiography (DR) technology has been widely applied to medical instruments such as an X-ray scanner for imaging thorax. A key component of a DR device is the flat panel detector for acquiring images. The flat panel detector's performance will influence the quality of the acquired DR images significantly.
At present, there are two kinds of flat panel detectors: amorphous selenium flat panel detectors and amorphous silicon flat panel detectors. As illustrated in FIG. 1, an amorphous selenium flat panel detector mainly consists of an amorphous selenium layer (not illustrated in FIG. 1), a pixel electrode 3, a storage capacitor 2 and a switching thin film transistor (TFT) 1. The incident X-ray makes the amorphous selenium layer to generate electron-hole pairs, and the electrons and holes move in opposite directions under the action of applied biasing electric field to form an electric current. The current passes through the pixel electrode 3 and brings about the stored charges in the storage capacitor 2, which are output to the readout circuit when the thin film transistor 1 is turned on. The amount of the stored charges output through each TFT corresponds to the dose of the incident X-ray. The amount of charges at each pixel point can be read by the readout circuit and the dose of X-ray at each pixel point can be further obtained.